Using optical microscopy/etch pit techniques for the delineation of defects in {100} Czochralski silicon wafers we have made a one‐to‐one correlation between bulk stacking faults in oxidized wafers and etch hillocks identified at the same sites before oxidation. Transmission electron microscopy of the hillock defects shows them to be clusters of precipitates ranging in size from 0.01 to 0.3 &mgr;m. A discussion of these stacking‐fault nucleation sites in light of previous work on ’’swirl’’ defects in float‐zone wafers and attempts at preoxidation gettering are also presented along with a model for the formation of the extrinsic stacking faults.